September 25, 2023

Engines part four: Why won’t it run?

Everytime I go to the field someone has a “faulty” engine – one that won’t start, or that dies in flight or on takeoff for some reason. Or at least they think they do. Fact is, it’s hardly ever the engine. People say the wildest things: “The whole setup is gone” (meaning cylinder and piston) “the bearings are busted”, “this damned engine is just crap”, “I heard [any brand engine]s are just crap”, “the engine was full of metal shavings when I opened it up for inspection” yada yada yada…

Hear this:

  • 8 times out of 10 it’s the fuel. Too much, too little or just not the right kind
  • 1 time out of 10 it’s the plug. (Which means it’s not an O.S. plug, or it’s a very old and worn O.S. plug)
  • 1 time out of 10 it’s the pilot (That would be you)

That’s 10 out of 10. My guess is, about 1 time in a hundred, something in the engine itself might actually be broken. In 20+ years of glow engine flying, that’s happened to me just once.

This is a series of general advice on engines describing my experiences. These posts are intended for those who still think about engines as a complete mystery -things I wish someone had told me before I had to spend the time to find out for myself. (YS mechanics and engine doctors already know this.)

It’s too lean! No it’s too rich! Etc…
There are many myths among pilots regarding engines. I hear people saying “maybe the bearings are broken” – well the engine starts just as easily with bad bearings so trust me it’s not that. People who blame bearings often do not fly enough to break them anyway, although admittedly you can do it in one flight if you are reckless enough. But this I know – when a bearing is broken you will hear it, and feel it when turning it over.

Cylinder peel is another myth, i.e. the peeling is real enough but the manufacturing problem people blame is highly unlikely. Bad fuel and running the engine piping hot is a more likely explanation. Pitts style mufflers and tiny canister mufflers are probably to blame, as are tightly cowled engine installations. Engines need to get the hot exhaust out, it they don’t they overheat. Simple enough, so why would you fit a smaller muffler than the original, and blame the manufacturer when your cylinder goes flaking on you?

A very common myth about certain makes of engines is that bits of metal shavings can be found inside them (most makes that are made in China have this reputation). Personally, I have never looked and will never look for stuff inside and engine, because chances are the factory that made them is a lot cleaner than your workshop. I believe if you find metal inside your engine it’s because you messed up disassembling it. Leave it alone unless you are an engine mechanic.

In fact, the only thing that comes to mind that actually happens every once in a while is a broken piston ring. If stored with a lot of castor oil inside for a long period the ring will get stuck and break once you try and start if at the beginning of the season. It’s highly unlikely that any other sort of damage is the cause of your engine not wanting to start.

Let me explain what actually happens when it won’t start or dies:

The engine needs a proper mixture of fuel and air to start. This means that if it doesn’t start, it has either too much or too little of one or the other. People are usually not aware that the engine is being flooded and this is easily overlooked because there is usually not much indication of it until the engine locks up. This happens to everyone, even pros struggle with this sometimes. But you can spot the clueless pilot easily: he’s the one blaming the engine maker, or claiming the bearings are broken. I’ve also seen people grinding away with starters at engines that are bone dry. Hey, did ya open the needle valve dude? Connect the fuel line wrong, plugging the vent line to the carb? I see it ALL THE TIME. Something I do every now and again is try to start with no air… meaning I’ve forgot the throttle cut-off switch from the flight before. Duh. But try and learn from it, and don’t blame the engine.

Glow plug:
It’s not just about using a proper plug – you gotta get power to it, and lots of it. Many 1.2 volt small glow clips can’t deliver enough current so make you life easier by investing in a proper glow driver which not only indicates if the plug lights up or not, but also how much current is drawn. The best thing is a power panel with adjustable current and an ammeter. You can also mess up a start by using a starter and glow driver from the same power source, one battery is not always able to handle the amps drawn by boths, so that the starter takes the power the glow clip should have gotten.

About plug types, the right plug means any reasonable hot plug made by O.S. I’m serious, I have tried every make of plug out there in my 20+ years of glow engine operation up to and including the mythical Enya #3, and I have not had much luck with any of them. O.S. is simply better, that’s all.

Pilot error also appplies to starting. But most of the time it’s just that people don’t try hard enough. It can be anything from not swinging the prop properly, to having to small throttle opening, closed needle valve and so on. And pussy-flipping the prop over like you’re afraid of it just won’t do – you have to swing it like you mean it.

So there. It’s you, your equipment or a combination of both -not the engine. Play the odds and check fuel/air and plug. Don’t ever talk bad about an engine or open it unless a seasoned pro has attempted to start it for you and failed.

Engines not running properly and stopping in mid air or on takeoff are a different story, one that I’ll get to in due time…

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